This invention relates to structural materials having low densities, and, more particularly, to a nonmetallic, low-density, syntactic foam material.
Low-density nonmetallic materials with good mechanical properties are required for a number of aerospace and other applications. In one example, radomes that house radar antennas must have sufficient strength to withstand aerodynamic forces. The material used to construct the radome cannot interfere with the signals transmitted therethrough. In another example, stiffened sandwich core structures are formed by placing a core of material between spaced-apart face sheets. The core is present largely to space the face sheets apart so that the structure has a high flexural rigidity. In such applications, extremely high strengths at ambient and elevated temperatures are not a requirement, but moderate strength is desirable.
In some of these applications, the materials of construction are preferably of as low a density as possible while achieving the required mechanical properties. The low density leads to reduced fuel consumption in aircraft uses. A low density and weight may also be desirable in specialized non-aircraft applications such as rotating machinery.
Structural metals of relatively low density such as aluminum have been widely used for many years. More recently, structural nonmetallic materials such as epoxies and graphite/epoxy composite materials have been developed and have entered service. Foamed polymeric materials have also found many uses. The latter class of materials have densities even less than the polymeric materials from which they are constituted, since a portion of the interior of the material is voids that are intentionally produced in the material.
The existing polymeric materials and foamed polymeric materials have some drawbacks, however. Most significantly, the foamed polymeric materials are somewhat less controlled than is desired. They also do not have sufficiently high mechanical properties for some applications such as radomes.
There is therefore a need for an improved nonmetallic, low-density material of good mechanical properties. The present invention fulfills this need, and further provides related advantages.